Expresses regret for what's said to be the extent (5)
I believe the answer is:
sighs
'expresses regret for' is the definition.
The answer and definition can be both to do with communicating as well as being verbs in their -s form.
Perhaps you can see an association between them that I don't see?
'said to be the extent' is the wordplay.
'said to be' shows a homophone (sound like).
'the extent' becomes 'size' (I've seen this before).
'size' is a homophone of 'SIGHS'.
'what's' acts as a link.
Can you help me to learn more?
(Other definitions for sighs that I've seen before include "Sounds despondent" , "Moans" , "Yearns" , "Bridge of - - (Venice)" , "gentle sounds" .)